The present invention relates to a system for the secret transmission of audio signals, comprising a coding arrangement, at least one transmission channel and a decoding arrangement.
From U.S. Pat. No. 3,610,828, (Technical Communications) filed on May 23rd, 1967 and granted on Oct. 5, 1971, it is known to code analog audio signals by modifying fragments of these signals, more specifically by either inverting or not inverting these fragments, depending on the polarity of a binary digital signal.
However, a person with comparatively simple equipment, for example a function generator and a demodulation arrangement, is capable of regaining the encoded message in original form and consequently the system offers a very limited secrecy of the transmission.